1. Field of the Invention
The present invention relates to an apparatus and a method for accessing a metadata, and more particularly, to an apparatus and a method for consistently accessing the same contents that are being asynchronously copied to several computers.
2. Description of the Related Art
The storage system, in which many computers are connected in a network, and then some computers among them store a metadata, while the rest of the computers store data, can be used for mass data storage under the Internet environment.
Under the storage system environment, a client acquires actual data by firstly finding a particular data server storing data that is required through the metadata server check, in which the metadata server stores the metadata, and then accesses the data server.
When one of metadata servers is operated in the storage system that store mass data, requests from many clients is concentrated in one of the metadata servers. As a result, there is a bottleneck phenomenon, such that performance of operation is degraded.
Therefore, operating clusters of many metadata servers in the large-scale storage system has processed the clients' requests to have scalability.
Each of the metadata servers configuring the metadata servers' clusters stores the same metadata. Even if a client accesses any metadata server, the client can acquire the metadata related to the required data.
However, there is a synchronizing problem of metadata servers for maintaining the metadata servers that store the same metadata. Specifically, the contents that are stored by each of the metadata servers become show a disagreement within a certain period until identically storing newly generated metadata into all the metadata servers.
In this case, if a client accesses the metadata server that is randomly selected in order to increase the scalability of the metadata processing, the case, in which the client cannot find a desired metadata, can be caused. In other words, it can be possible that the data just generated cannot be found. Meanwhile, on the contrary of this, it can be possible that a client misjudges that the data just deleted exists.
U.S.A. Patent Laid-Open Publication No. 2007/0078809 A1 discloses a method for managing and using data storage that is dispersed. The patent application discloses using a peer-to-peer way in order to secure high serviceability for supplying data to a user. If a client asks a file, the system calculates the location that stores the file, and then finds the closest source for acquiring the file. After a client receives the file from the relevant source, the client copies the file to himself or herself. As a result, a client can immediately use the file for a further quick search, and the copied file also functions as a source that can be supplied to other clients. The patent application discloses a method for increasing data serviceability. However, there is not a specific process for supplying the consistent results to a client in a circumstance that the same contents are asynchronously copied to many servers.
U.S.A. Patent Laid-Open Publication No. 2009/0210640 A1 discloses a method for eliminating data duplication and increasing efficiency of a reading operation in a circumstance when a plurality of storages exist. The patent application discloses a file configuring a plurality of blocks. In a circumstance when a plurality of files is stored, when the blocks having the same contents with an already existing block are stored, it may be attempted that the data duplication can be solved by maintaining point information indicating that the existing blocks having the same contents instead of delicately storing the same file. In addition, when searching the desired file from the data storage, the search order should be selected based on the physical location between the blocks configuring the file, and then if the same block with the block to be now read is already loaded in a buffer, it should not be read. The patent application discloses a method for efficiently reading when existing in the same blocks, but does not disclose a method for supplying consistent results to a client in a circumstance that the blocks having the same contents are copied.